i already have my 18K/W TO220 slip-on-heatsinks installed. Fun-fact, i've just measured exact temps (54*C @ 7812), then measured some on... the one 1117-5V is at 48*C too, followed by the AK4393 @ 45*C. I somehow have a feeling that this is a little bit much for this little chip, right?

Oo what could be wrong? And how is it for you - do your AKs, 1117-5Vs and 7812s hot?

Hot for a component is usually specified on the datasheet.

Having the heatsinks installed doesn't mean correctly installed. Heat has to transfer to the heatsink, and the whole has to be at the same temperature. If the component is hotter than the heatsink, then the transfer is not happening as it should.

If the whole is at the same temperature and still hot to touch, then you need a larger heatsink. And so on.

But the current we are talking on this project are very low, so parts, particularly the SMDs on the board, shouldn't be hot at all. Perhaps you do have some sort of oscillation going on, though I doubt it might be because of low esr capacitors, except on some border case. Change the capacitors at the output of the regulators and see what happens, or leave just a film bypass cap.

I'm still at a loss where i could find information on why lower-esr capacitors should be bad for regulators?

Later I'll search and post something about it

Quote:

Originally Posted by NebuK

*EDIT: i've just checked the datasheet of the on-semi 7812 you like, they say:
"""An input bypass capacitor should be selected to provide good
high−frequency characteristics to insure stable operation
under all load conditions. A 0.33 mF or larger tantalum,
mylar, or other capacitor having low internal impedance at
high frequencies should be chosen."""

Having the heatsinks installed doesn't mean correctly installed. Heat has to transfer to the heatsink, and the whole has to be at the same temperature. If the component is hotter than the heatsink, then the transfer is not happening as it should.

If the whole is at the same temperature and still hot to touch, then you need a larger heatsink. And so on.

Well, i do measure 55*C on the chip and roughly 52*C on the heatsink just now - i think i've smeared enough high-quality thermal compound in there (too much isn't good after all...). The 78XX are specified up to 120*C(!) absolute max, so ~50-60*C should be way in the safe range, right? I'm more worried about the AK @ 45*C... ;/

Quote:

Originally Posted by carlmart

But the current we are talking on this project are very low, so parts, particularly the SMDs on the board, shouldn't be hot at all. Perhaps you do have some sort of oscillation going on, though I doubt it might be because of low esr capacitors, except on some border case. Change the capacitors at the output of the regulators and see what happens, or leave just a film bypass cap.

So you propose to completely remove the (1117-5v?) electrolytics (which would be C31, right?), or also maybe also the big buffers for the 7812 (C38?), correct? (i'm a little worried i could break something here, so i'd better try asking some dumb questions before i'll break something...).

Well, i do measure 55*C on the chip and roughly 52*C on the heatsink just now - i think i've smeared enough high-quality thermal compound in there (too much isn't good after all...). The 78XX are specified up to 120*C(!) absolute max, so ~50-60*C should be way in the safe range, right? I'm more worried about the AK @ 45*C... ;/

Probably an obvious question, but I have to do it: did you check that the heatsink is isolated from all pins, particularly the middle one?

Quote:

So you propose to completely remove the (1117-5v?) electrolytics (which would be C31, right?), or also maybe also the big buffers for the 7812 (C38?), correct? (i'm a little worried i could break something here, so i'd better try asking some dumb questions before i'll break something...).

Where do I say remove the regulator 1117-5v? I say remove the large electrolytic capacitor at the output of 78XX and leave the film cap. This is just to see if it's the capacitor which is making any problem.

The SMD regulator should be just warm to touch.

In any case, 55 degrees C is not that high. Tighten up the screw holding the heatsink to the regulator. Temperature should be the same on both if transfer is OK.

I've read all the 78xx regulator datasheets i could find. If anything, they state that lowest esr capacitor types should be used to ensure lowest noise operation of the regulator as well as long capacitor life and slow degradation (from Murata).

Martin Clark of Acoustica,com has a 4 part tutorial on the use of 3 pin regulators, particularly focusing on the LM317/337 adjustable types. This tutorial is worth reading, especially part 3 which contains a discussion on the merits of the ESR value of the output cap. Even though Martin is discussing the adjustable regulator, a lot of what he says about output capacitor ESR is relevant to the fixed regulators.

Martin argues that Arbitrarily-low ESR is not necessarily a good thing and suggests that a good quality electrolytic output capacitor with an ESR of about 0.3R will be "critically damped" and suitable for the LM317. But you also need to read the notes.

Probably an obvious question, but I have to do it: did you check that the heatsink is isolated from all pins, particularly the middle one?

Where do I say remove the regulator 1117-5v? I say remove the large electrolytic capacitor at the output of 78XX and leave the film cap. This is just to see if it's the capacitor which is making any problem.

The SMD regulator should be just warm to touch.

In any case, 55 degrees C is not that high. Tighten up the screw holding the heatsink to the regulator. Temperature should be the same on both if transfer is OK.

Hey,

thanks again - i wouldn't have removed the 1117-5v, i asked whether i should remove the 100uF cap buffering the 1117-5v supply in addition to the large 2200uF of the 7812. Sorry if i got it wrong, i know my english can suck sometimes .

Thanks @ jnewbold too, will read later...

Regards
-Dario

*EDIT: I know 55*C isn't hot for a 7812/1117, what i'm worried about is the AK @ ~45*C - this chip has a maximum rating of 85*C and its cold in my room in winter, so ... i just wonder whether this is ok? on the other hand typical is 60mA@5V + ~10mA@3.3V? it *should* get a little warm from that...?)

Last edited by NebuK; 22nd January 2012 at 10:18 PM.
Reason: forgot info

1.3 Output Capacitor
The output capacitor is critical in maintaining regulator stability,
and must meet the required conditions for both minimum
amount of capacitance and ESR (Equivalent Series
Resistance). The minimum output capacitance required by
the LM1117 is 10μF, if a tantalum capacitor is used. Any
increase of the output capacitance will merely improve the
loop stability and transient response. The ESR of the output
capacitor should range between 0.3Ω - 22Ω. In the case of
the adjustable regulator, when the CADJ is used, a larger
output capacitance (22μf tantalum) is required.

Standard voltage regulators (like LM78xx) are (much) less affected by the problem but, regarding heat, it must be taken in account that a big value low-esr cap require much more current to maintain its charge, thus increasing regulator's heat generation.

So my recommendation was right (better a non low-esr cap at the output of regulator) for both LDO and standard regulators but for the latters stability it's not a problem while overheating remain a problem.

i've just toyed around with the 2200uF caps of the "first level" regulators, the 7812, 7912 and 7809 a little. Taking them out has no effect whatsoever. I haven't dared to get rid of the 1117-5v, the datasheet vetoed...

There was no effect measurable. After ~30min listening my 7812 was on ~50*C again, the 1117-5v and AK4393 were at ~45*C. A friend also found a neat paper which is basically about those AKs - http://www.scheme.ro/files/diverse/d...ta_mutibit.pdf. Judging from this the temperature is totally normal. As when putting my power-meter serial in trafo -> dmm -> dac-board for every trafo winding i observer 30mA to the 7812, 25mA to the 7912 and something very low to the 7809. This also correlates to the power estimates given by the datasheets of the 4 sinks (receiver, dac, opa and 74hc04). So i guess i'm not really having a problem here after all? From what i understand at least?